The climate is changing. It was bound to happen, whether humans intervened or not. The Earth has gone through so many climate changes over its 4.5 billion years of life that it's enough to make your head spin — or melt, or get eroded by corrosive elements in the atmosphere, depending on what geological era you lived through. Over 25 million years ago, icy Antarctica was a tropical paradise. But as it and the north pole froze over, the planet entered a cooler period that was ideal for the evolution of humans and many other creatures in our current ecosystems.

So if we want to survive, we need to do something profoundly unnatural. We need to maintain the climate in its current state. And we'll do it by conducting the greatest geochemistry experiment in the history of the world. Some call it geoengineering. Here are ten ways this could happen.

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Maintaining the climate in an ideal state for us means keeping things cool at the poles. That's where geochemistry comes in. Put simply, the more carbon there is floating around in the atmosphere, the warmer things get. So, to stop things from heating up into a greenhouse climate, we need to maintain present levels of carbon in the atmosphere. We also need to keep the oceans fairly alkaline. The more carbon there is in the atmosphere, the more gets dissolved in the oceans to become carbonic acid. You've probably heard this process called "acidification." It kills sea creatures who occupy core nodes in the food web, and once they go, the whole thing unravels and a lot of species die rapidly.

So as we go through these options, remember our key goals: 1) Keep it cool; 2) Less carbon in the air; and 3) Less acidification of the oceans.

1. Stop using fossil fuels
Environmentalists like Bill McKibben may hate the idea of geoengineering, but even he and his cohort can get behind this idea. The Industrial Revolution and its aftermath changed the climate by releasing a lot of carbon into the air. If we stop using fuels that release carbon, the climate will very slowly return to its cooler state. Interestingly, many of the previous climate changes on the planet were caused by mega-volcanoes that released gases and carbon that strongly resemble what we're releasing from our factories and vehicles today. Very crudely, you might say one industrial revolution equals one megavolcano. We know the planet recovered from the damage of these mega-volcanoes, but it often took millions of years. So once we stop burning fossil fuel, how do we reduce the time to recovery from millions of years to hundreds? That's where these other geoengineering ideas come in.

2. Make the clouds more reflective
A simple way to cool the planet down is to make clouds more reflective. Already, clouds are a major way the planet cools itself because they reflect light back into space. There is a lot of evidence that aerosols from cargo ships have helped make clouds more reflective, by adding more particles to clouds that reflect light even better than typical clouds do. Some scientists have proposed seeding clouds with sulfate particles, which are highly reflective, or perhaps with some yet-to-be-discovered "particle X" which would float in the stratosphere for years, reflecting light back into space. There are two big problems with this idea. One, we aren't entirely certain how hyper-reflective clouds would affect weather patterns. But more importantly, this is only a short-term solution. We'd have to be pumping particles into the clouds constantly. If we kept using fossil fuels during this time, the planet would become a greenhouse timebomb — if we were ever unable to keep the clouds reflective, the planet would heat up extremely rapidly and disasters would follow. So this is only a short-term solution to be used in connection with systems that would remove carbon from the atmosphere.

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3. Giant space reflector
Instead of seeding clouds with sulfide particles, why not just install a giant reflector in space, around the whole planet? I love this idea because it's marvelously science fictional, but I've read a number of great SF novels where there are huge solar reflectors that are ripped apart in battle and leave the planet more vulnerable than ever. So, nice idea, but if it fails in any way we're back to that super-rapid greenhouse situation.

4. Planting trees
Here's another idea that the most luddite of the environmentalists can get behind. Trees are the planet's natural filtration system. They take carbon dioxide out of the air and release oxygen into it. Part of the reason our climate is changing is that we've cleared away a lot of the forests and jungles that do this global climate filtering for us. So, let's plant more trees again — especially mangroves.

5. Enhanced weathering
Weathering, or the process of wearing down mountains and Earth with wind and rain, is another one of the planet's natural filtration systems. As rocks and pebbles are broken down by weather, they pull carbon out of the atmosphere via a complex chemical process. Then they are washed into the sea, where they fall to the seafloor with their carbon load. Your carbon is now at the bottom of the ocean, where it stays for millions of years. Some geoengineers propose speeding this process up, by spreading pre-weathered rocks out in various locations. Instead of weathering processes that take millions of years, this "enhanced" process could pull carbon out of the air very quickly. If we did this while making the clouds more reflective, we could eventually pull enough carbon out of the air that we could stop messing around with the clouds — we'd have reduced the carbon load enough that more light wouldn't mean an instant greenhouse.

6. Ocean fertilization
This idea has already been tried a few times, most recently by a rogue geoengineer in Canada. The idea is that you dump a lot of iron powder into the ocean, which is a favorite food of cyanobacteria and other single-celled sea creatures. You cause a gigantic bloom of these little guys as they feast on that yummy mineral. Then, like trees, they suck carbon dioxide out of the air. The hope is that when they die, they sink to the bottom of the ocean and take that carbon dioxide with them. Unfortunately, when scientists have tried small-scale versions of ocean fertilization, it hasn't worked — the dead bodies of the cyanobacteria don't actually sink deeply enough into the ocean bottom, and they wind up releasing that carbon back into the atmosphere.

7. Ocean alkalinity enhancement
One of the biggest carbon sinks in the world is the ocean. That's why a lot of these projects' happy ending is "and then it goes to the bottom of the ocean, never to be heard from again." The problem right now is that the ocean has absorbed so much carbon that it's becoming acidic and incapable of absorbing more carbon without major damage. But what if we could make the ocean less acidic again? That would mean A) creatures who like an alkaline environment would thrive and B) the ocean could start absorbing carbon again. This project would involve dumping a huge amount of limestone, silicates, calcium hydroxide, or other alkaline-inducing substances into the ocean, in the hope that they would maintain the water's pH at a level that's better for life and the carbon cycle.

8. Air purification
If all those trees and cyanobacteria and enhanced weathering and ocean alkalinization are still not keeping the climate at the right level for you, why not get really speculative? Some engineers believe we could invent giant air filtration systems that would pull carbon dioxide out of the air, then pump it into vast caverns beneath the Earth's surface. There, under great pressure, the carbon dioxide would — yes, you guessed it — remain beneath the ground for millions of years.

9. Stratospheric aerosols
Making the clouds reflective isn't good enough for you? Well, why not pump those reflective particles above the cloud layer into the stratosphere? Unlike cloud seeding, this idea has the advantage that particles can remain suspended in the stratosphere for possibly a couple of years. Some geoengineers fantasize about a potential "particle X" whose shape could keep it suspended for up to 20 years, reflecting light back to the sun and cooling Earth down. The problem, however, is the same as with cloud albedo enhancement. Eventually the particles are gone, unless you keep pumping them up there. And if we keep burning fossil fuels, the loss of those reflective particles will mean a runaway greenhouse.

10. Burn biofuel
When you burn biofuel, you get green energy and you get a lot of burned plant material, AKA carbon. Many biofuel advocates point out, rightly, that this could create a nice carbon sequestration system. You get your energy, and you bury the carbon-rich byproduct known as "biochar." This enriches the soil, and has the effect of keeping that carbon out of the air and in the ground where it belongs.

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Most geoengineers believe that we should use many of these strategies at the same time to maintain a healthy climate for humans and all the creatures who share our food web. And the very first thing we need to do is stop using fossil fuels. Then we can start mitigating the damage that's already been done.